The present invention relates to a method for fabricating a winding type lithium ion secondary battery. In particular, the present invention relates to a method for fabricating a lithium ion secondary battery using a winding type electrode plate assembly formed by integrating a separator with electrode plates.
As lithium ion secondary batteries mainly used have been batteries having a structure obtained by winding up a positive electrode plate and a negative electrode plate together with a separator such as a microporous polyethylene sheet to prepare a winding type electrode plate assembly and then accommodating this electrode plate assembly and a non-aqueous electrolyte in a predetermined case.
Moreover, from the perspective of accommodating properties in devices, rectangular batteries having a shape obtained by: applying pressure to an electrode plate assembly wound up in cylindrical form or winding up an electrode plate assembly in flat form to prepare a flat winding type electrode plate assembly; and accommodating it in a flat metal battery case of a rectangular or long-elliptic cross section, have been preferably employed as the winding type batteries.
Principally from the viewpoint of safety, lithium ion secondary batteries, so-called polymer batteries, having a configuration of disposing a porous polymer layer between a positive electrode plate and a negative electrode have been attracting attention in recent years. A typical lithium ion secondary battery of this type is a laminated type battery comprising a laminated electrode plate assembly obtained by laminating and integrating the platy positive electrode plate and negative electrode plate via the porous polymer layer.
Furthermore, because of an increasingly demand for safety associated with thinner separators for higher capacity, winding type batteries obtained by forming a porous polymer layer on an electrode plate and then winding up the whole to prepare a winding type electrode plate assembly have been proposed in, for example, Japanese Laid-Open Patent Publications No. 11-345606 and No. 11-86844. In the process of preparing the winding type electrode plate assembly, however, the entire electrode plates can be integrated only after the electrode plate assembly is wound up.
On the contrary, since an electrode plate assembly prepared by integrating and winding up one of the electrode plates and the separator is not integrated as a whole, expansion and shrinkage of the electrode plates due to charge/discharge cycles, or generation of gas during storage at high temperatures and the like causes the gas to remain within the electrode plate assembly or the electrode plate assembly to deform, leading to deterioration in characteristics.
From the aforesaid perspective, it is an object of the present invention to provide a method for fabricating a lithium ion secondary battery capable of suppressing deterioration in cycle characteristic as well as storage characteristic resulted from expansion and shrinkage of an electrode plate due to charge/discharge cycles or generation of gas during storage at high temperatures and the like, by using a flat winding type electrode plate assembly, which can be wound up and further is integrated at the time of completion thereof.